Railway tank cars are one medium for bulk transport of various industrial liquids and gases, including hazardous fluids. Such tank cars have domes where valve operators, such as handles and levers, for various fluid-handling valves are located. The valve operators are external to the tank and housed within a protective housing that has a hinged lid or cover that when swung opened, or removed entirely depending on the particular dome construction, exposes the valve operators so that personnel can access them. The bodies of the valves themselves may be mounted on the bottom wall of the housing, but in some tank cars, they are mounted elsewhere but still operated by a handle or lever within the housing.
One or more of the valves is opened during certain procedures involving loading and/or unloading of fluid into and/or from the tank. In preparation for such procedures, a valve operating assembly having a power actuator, such as an air motor, is hoisted onto the dome where it is then properly placed to associate a coupling attached to an output shaft of the power actuator, an adapter for example, with a valve operator. Depending on the specific configuration of the valve operating system and assembly, the power actuator can be controlled in one or more of various ways: directly at the dome by attending personnel; remotely from a remote location, either by attending personnel, or automatically; uni-directionally to only close an open valve; uni-directionally to only open a closed valve; bi-directionally to either close an open valve or open a closed valve.
One type of valve operator comprises a handle that is turned about a vertical axis to open and close the valve. Such handles have different geometries, and hence unique adapters that removably attach to the power actuator output shaft may be required for particular valve handles. The axis of the output shaft of the power actuator can be coincident with the axis about which the valve operator turns, thereby enabling the adapter alone to interface between them. An example of a valve closure system and assembly for closing valves having such handles is disclosed in commonly owned utility patent application, VALVE CLOSURE SYSTEM AND VALVE CLOSURE ASSEMBLY, application Ser. No. 10/418,693, filed 18 Apr. 2003.
Another type of tank car dome valve is a ball valve whose operator comprises a lever that is swung about a generally horizontal axis to open and close the valve. A typical range of motion for the lever is 90°, and so a valve closure system and assembly for such a valve must be capable of moving the lever over that range of motion with sufficient and appropriate torque throughout the entire range. Some lever-operated ball valves are fully open when the lever is substantially vertical and fully closed when the lever is substantially horizontal. Others are exactly opposite, being fully closed when the lever is substantially vertical and fully open when the lever is substantially horizontal. Still others may be open or closed when their levers are inclined to both horizontal and vertical. The sizes and shapes of the levers may also vary to some extent.
In certain tank cars, the bodies of certain valves may be disposed in locations other than the dome, such as at the bottom of the tank; yet their operators may be located within the protective housing at the dome.